1. Field of the Invention (Technical Field)
The present invention relates to an electronic control which is completely incident within a cordset plug or plug-in module, and which enables the distributed control of an appliance. User inputs are made at a remote location that is located either at the actual appliance or in-line between the appliance and the plug or plug-in module. Control signals are transferred bidirectionally via the two power conductors that connect the plug (or module) to the user input module and load. As a side benefit, electrical shock and electric arc fault protection may be provided at the power inlet to the appliance. A key feature of the invention is the way in which information is transferred via “deadzones” that are imposed upon the AC load current. If there is some current flow during a time when a deadzone should occur, this is indicative of a fault condition, either unintentional (as when an undesirable leakage path to ground occurs) or intentional (for example with faults that are deliberately applied using switch closures to impose momentary fault conditions). By controlling the deadzone times to have different lengths, then user inputs, appliance status, and other information may be sent to a remotely located controller. The technology is further adaptable to communication with a receptacle outlet, whereby information may be communicated between an appliance and a household network via control signals imposed upon the power lines.
2. Description of Related Art
Any electrical device (the “load”) requires the flow of electrical current in order to operate. The electrical device receives electrical energy from one terminal (the so-called high voltage or “hot” side) of an electrical outlet or source, electrical current flows to the device through an electrical conductor or wire (the “hot conductor”), this current passes through the load and is then returned through another wire called the neutral conductor which then connects to a second power delivery terminal. The neutral conductor is said to have a “ground” potential because the neutral conductor will be electrically connected to ground at some point in an electrical distribution system.
The two wires connecting source and load may have a coating of rubber or some other electrical insulating material or they may be bare, in which case, air, which is a good electrical insulator, functions to inhibit electrical current flow outside of the wire. Since the human body can conduct the flow of electrical current, if a person comes into contact with one electrified object while simultaneously making contact with a second electrified object having a different voltage, then an electrical leakage current that is proportional to the difference will flow through the person and may cause injury or death. If the second object that a person comes in contact with is electrically connected to the earth (ground) then this condition is called a ground fault. In electrical appliances, a potential fire hazard can occur when electrical current flows across a leakage path from one electrified conductor to another, resulting in a luminous discharge. This is known as an arc (or arcing) fault.
Electrical current is the flow of electrons. Electrons are neither created nor destroyed so any functioning electrical appliance will require both an entry path for electrons and an exit path for electrons in order for the electrical current to flow. In an electrical appliance, electrons may exclusively enter on one path and exit on a second path. This is called direct current or DC operation. For most household appliances that operate from a plug, electrons will sometimes enter path one and exit path two and sometimes enter path two and exit path one. This is known as alternating current or AC operation.
Although the two conductors that deliver power to a home AC appliance in the U.S. are generally designated as “hot” and “neutral”, in an AC system, the hot conductor will cyclically have a more positive voltage than the neutral for half of the time and will cyclically have a more negative voltage than the neutral for half of the time, having a momentary value of zero each time the voltage passes from positive to negative and negative to positive. The times at which the voltage potential between hot and neutral is zero is known as the voltage zero crossing. In the absence of a fault, the current flow through the two power delivery conductors will always have the same magnitude but opposite polarities. In an AC system, the current flow will vary in a sinusoidal manner, flowing in one direction into the load for half the time and in the opposite direction for half the time. When the current flow is zero, this is known as a zero crossing of current. For a load that is predominately resistive, or that is controlled to have the profile of a resistive load, the zero crossings of current will occur at the same times as the zero crossings of voltage.
In many electrical appliances and virtually all electrical distribution systems, electrical elements called fuses are employed to limit the maximum current that can be delivered. A fuse is a two terminal, two-state device that, in normal operation, acts as a short circuit. When relatively high currents are passed through a fuse, heating within the fuse causes a fusible element to open, thereby permanently interrupting power flow through the fuse and causing the fuse to permanently enter a second, “open” state. When used in an electrical appliance, fuses are sized to handle the normal operating currents that are expected to flow in the appliance. Then, in the event of an abnormal operating condition, such as a short circuit within the appliance, the high electrical currents that flow through the fuse serve to cause the fuse to go into an open circuit condition or “blow” the fuse, thereby interrupting power. For example, in an appliance that never exceeds 1 ampere of electrical current in normal operation, it might be appropriate to use a fuse having a rating of 2 amperes. The fuse will act as a short circuit during normal operation, and in the event of a so-called “fault”, such as when frayed electrical conductors from a damaged cord bridge between two power conductors, the fuse will protect the appliance by becoming open.
While a fuse offers some level of protection against heavy currents in an appliance, and consequently offers protection against the electrical fires that can occur when an appliance fails, it does not offer a high level of electrical shock protection to people. The reason is that electrical currents as low as 5 to 10 milliamperes can be lethal and this level of electrical current is far below the normal operating currents in most electrical appliances. In order to protect against low level (but potentially lethal) electrical leakages, a device called a ground fault interrupt is used.
A heater is a type of electrical load that is essentially a resistor. A wire having a relatively high resistance is configured so as to transfer heat in an efficient manner—through a barrel of glass or a metal tube in an aquarium heater or curling iron; and distributed more or less evenly over a large area in a heating pad or electric blanket. As electrical current flows though the resistance of the heater, it generates heat. This heat power may be expressed in watts and is calculated as I2R, where I is electrical current in amperes and R is resistance in ohms. In the event of a damaged heating element, the load may draw less electrical current but can generate a great deal of heat in the area local to the damage. This damaged area can lead to fires or burns.
U.S. Pat. No. 3,564,203 (Naoi, et al.) discloses an automatic temperature control device for an electric blanket wherein a relay is used to regulate the electrical current applied to the blanket. The circuit requires four wires connecting the controller to the load.
U.S. Pat. No. 3,597,590 (Fleming) discloses an electronic control for a heated device in which the power is controlled to turn on at the zero crossings of the AC line, thereby minimizing radio frequency emissions.
U.S. Pat. No. 4,359,626 (Potter) discloses an electric blanket control that incorporates an capacitive “occupancy sensor” that is said to automatically remove power from the blanket if the blanket is not in use. One embodiment of this invention incorporates a ground fault interrupt safety circuit to protect against electrical leakages to ground.
U.S. Pat. No. 4,436,986 (Carlson), U.S. Pat. No. 5,451,747 (Sullivan et al) and U.S. Pat. No. 5,770,836 (Weiss) disclose an electric blanket safety circuit for PTC based heaters, that utilizes gas tubes to sense voltage imbalances caused by open or short circuits and to conduct sufficiently high currents to blow a series connected fuse. One problem with this approach is that while it protects against a catastrophic failure in the electric blanket, it will not detect or prevent lower level electrical currents that, while insufficient to blow a fuse, are high enough to cause electrical injury or electrocution. An additional problem with this approach is that it necessitates four conductors connecting between the load (the heater) and the controller. An additional disadvantage is that the approach requires that the heater load contain positive temperature coefficient (PTC) elements. An additional disadvantage is that while these designs provide some degree of electrical shock protection at the heating elements, they do not provide protection within the electrical conductors connecting controller to heater or within the electrical conductors connecting plug to controller.
U.S. Pat. No. 4,549,074 (Matsuo) discloses a temperature controller incorporating a rapid initial heat. The invention is electronically complicated and requires five electrical conductors attaching the electric blanket to the controller.
U.S. Pat. No. 4,885,456 (Tanaka et al.) discloses a temperature controller whereby a thyristor is controlled to deliver power to a load immediately prior to a zero crossing of the AC line, thereby avoiding electromagnetic noise interference.
U.S. Pat. No. 5,708,256 (Montagnino et al.) discloses a heating pad controller with variable duty cycle for temperature adjustment.
U.S. Pat. Nos. 5,844,759, 5,943,198 and 5,973,896 (all to Hirsh et al.) describe a solid state ground fault and arc fault detection and interruption technology for an electrical appliance that has two parts, one part which resides in or near the load (the load conditioner) and a second part which is located at or near the plug. The load conditioner injects a deadzone in the current flow during each half wave AC cycle. A sensing circuit in the plug looks for the presence of that deadzone each half cycle. If there is leakage around the load conditioning module (indicating a ground fault or arcing fault) this is indicative of a potentially dangerous electrical condition and the current flow is interrupted at the plug. U.S. Pat. No. 6,560,079 B1 (to Hirsh et al) further extends this technology to the detection of transposed AC conductors (i.e., neutral and hot conductors are swapped) or to the detection of an open ground condition in a grounded appliance.
The present invention is preferably designed for use in an appliance cord for AC appliances. In its preferred embodiment, it is a two part system. The electrical interruption means and primary control are located within the plug. User inputs are more conveniently located either at the load or within an in-line control module. User inputs, including the adjustment of switch position and/or momentary button presses, are encoded into signals that are superimposed upon the AC line and that can be intercepted and interpreted at the control electronics within the plug, whereupon, the control electronics within the plug actually implement appliance control functions including power settings, initial heat-up, and automatically shut off. In addition, this two part system may be used to provide electrical ground fault protection and electrical arc fault protection within the appliance. The same two bidirectional communications approach may also be used between the appliance and a transceiver located in a wall outlet, thereby allowing status and control information to be passed from appliance to a home network.